Aleutian Island Report Card - 2020

Aleutian Islands 2020 Report Card (pdf)

Region-wide

  • The North Pacific Index (NPI) was strongly positive from fall 2019 into 2020 due to the relatively high sea level pressure in the region of the Aleutian Low, which was displaced to the northwest, over Siberia, and caused persistent warm winds from the southwest. Positive NPI is expected during La Niña but its magnitude was greater than expected, though not as large as in 2018.
  • The Aleutians Islands region experienced suppressed storminess through fall and winter 2019/2020 across the region, favoring seabird foraging.
  • The Alaska Stream appears to have been relatively diffuse on the south side of the eastern Aleutian Islands for the eighth consecutive year. This is unusual in an area characterized by discrete and intense events. Low eddy kinetic energy prevailed throughout the chain.
  • Although the sea surface temperatures cooled off in 2020, relative to the 2014-2017 warm period, the overall temperature was still warm due to heat retention throughout the water column. The eastern Aleutians Islands was under an almost year long heatwave during 2019, which was significantly less intense in the central and western islands. Temperatures during 2020 were moderate across the archipelago.
  Mean Trend  
*North Pacific Index (winter anomoly)
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Figure 1: The winter North Pacific Index times series. * indicates time series updated in 2020.

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Figure 2: The Aleutian Islands ecoregions.

Western Aleutian Islands Ecoregion 2020

  • Temperatures have been much milder in this area, offering a potential refuge for populations from farther east where heatwaves have occurred in recent years. While cooling at the surface, warm water still prevailed in subsurface layers 100-250 m deep during 2020.
  • The reproductive success of five planktivorous seabird species at Buldir Island was average to high in 2019, indicating that overall zooplankton availability was sufficient to support reproductive success in 2019 and potentially other plankton eating commercial species.
  • Forage fish trends, as indicated in tufted puffin chick meals, have varied over the long term, with episodic peaks lasting 1-2 years. In general, sand lance have been absent since 2009, and age-0 gadids have not been seen in great abundance since 2006. Tufted puffins experienced reproductive failures in 2017 and 2018, but had average reproductive success in 2019, signaling potentially favorable condition for fish foragers. Both horned puffins and glaucous winged gulls had high reproductive success, suggesting that forage fish availability was diverse and sufficient to raise chicks in 2019, and potentially other fish eating predators and commercially important groundfish.
  • Steller sea lion numbers remained below their long-term mean when last estimated in 2019, although there has been no significant trend in the past 5 years. The 2016 estimate was the lowest in the time series.
  • There are no schools in the western Aleutian Islands ecoregion.
  Mean Trend  
*Western AI Least Auklet reproductive success
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*Western AI Crested Auklet reproductive success
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*Western AI Ammodytes in Tufted Puffin diet
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*Western AI Gadids in Tufted Puffin diet
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*Western AI Hexagrammids in Tufted Puffin diet
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Western AI Pelagic Forager Biomass
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Western AI Apex Predator Biomass
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Western AI Otter Density at Attu
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*Western AI SSL non pup counts
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Western AI Habitat Impacted by Trawls
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Figure 3: Western Aleutian Islands ecoregion indicators. * indicates time series updated in 2019 - there were no 202 updates.

Central Aleutian Islands Ecoregion 2020

  • The most recent data available for sea otters show no trend but is from 2015. There is some concern in the region as to their current population trend; however updated assessments should be available next year.
  • Counts of non-pup steller sea lions remain below the long term mean, however the population is either stable or slightly increasing; though the trend is not the same in all rookeries.
  • Both Adak and Atka chools in the central Aleutian Islands have experienced a slight uptick over the past 2 years, getting away from the 10-student threshold that risks closure of the schools, thereby offering more stability to families living in those communities.
*indicates time series updated in 2020 Mean Trend  
*Central AI Pelagic Forager Biomass
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*Central AI Apex Predator Biomass
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Central AI Otter Density
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Central AI SSL non pup counts
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*Central AI school enrollment
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Central AI habitat impacted by trawls
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Figure 4: Central Aleutian Islands ecoregion indicators. * indicates time series updated in 2019 - there were no 2020 updates.

Eastern Aleutian Islands Ecoregion 2020

  • Although the time trends for the fish indicators don't show it, four out of six monitored fish-eating or piscivorous seabird species had high reproductive success in 2019, while the rest had an average year. Together, this made 2019 one of the most successful years in recent history; despite the year-long marine heatwave in this ecoregion. This broad reproductive success across species signaled favorable environmental conditions to feed and raise chicks, as well as potentially increased fish prey availability for other predators, including commercial groundfish.
  • There are no available data for sea otters in the eastern Aleutians ecoregion.
  • In contrast to the other regions in the Aleutian Islands, non-pup counts of Steller sea lions continue to steadily increase. The recent estimates in 2019 have been above the long-term mean and are continuing an increasing trend. Counts were largely stable through the 1990s, but have been increasing a rate of 2% per year, offsetting the declines observed in the other regions of the Aleutian Islands.
  • School enrollment has increased since the recent low enrollment in 2014-15. This primarily reflects trends in Unalaska, whereas the small communities have either closed schools (Nikolski) or are at risk of closure (False Pass and Akutan).
  Mean Trend  
*Eastern AI Ammodytes in Tufted Puffin diet
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*Eastern AI Gadids in Tufted Puffin diet
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*Eastern AI Hexagrammids in Tufted Puffin diet
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Eastern AI Pelagic Forager Biomass
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Eastern AI Apex Predator Biomass
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*Eastern AI SSL non pup counts
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*Eastern AI School Enrollment
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Eastern AI Habitat Impacted by Trawls
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  2014-2018 Mean   2014-2018 Trend
  1 s.d. above mean   increase by 1 s.d. over time window
  1 s.d. below mean   decrease by 1 s.d. over time window
  within 1 s.d. of mean   change <1 s.d. over time window
  fewer than 2 data points   fewer than 3 data points

Figure 5: Eastern Aleutian Islands ecoregion indicators. * indicates time series updated in 2019 - there were no 2020 updates.